1. Field of the Invention
The present invention relates to ceramic susceptors employed to retain and heat wafers in semiconductor manufacturing equipment in which predetermined processes are carried out on the wafers in the course of semiconductor manufacture.
2. Description of the Background Art
A variety of structures for ceramic susceptors employed in semiconductor manufacturing equipment has been proposed to date.
For example, a semiconductor wafer heating device equipped with a ceramic susceptor in which a resistive heating element is embedded and that is installed within a reaction chamber, and with a pillar-like support member provided on a surface of the susceptor apart from its wafer-heating face and that forms a gastight seal between it and the chamber, is proposed in Japanese Pre-Grant Pub. No. H06-28258.
In order to reduce manufacturing costs meanwhile, a transition to wafers of larger diametric span—from 8-inch to 12-inch in outer diameter—is in progress, along with which the ceramic susceptors that retain the wafers are turning out to be 300 mm diameter or more. At the same time isothermal ratings within ±1.0%, more desirably within ±0.5%, in the face of wafers being heated by the ceramic susceptors are being called for.
In response to demands for enhanced isothermal properties as such, research has been made into improvements in the circuit patterns for the resistive heating elements provided in ceramic susceptors. Consequent on the enlarging of the diametric span of wafers and ceramic susceptors, however, realizing the demands just mentioned in terms of wafer-surface isothermal quality is proving to be difficult.
The ceramic-susceptor face that carries a wafer is typically formed as a simple plane, wherein a semiconductor wafer is retained and heated atop the flat wafer-retaining face. Nevertheless, because there is thermal radiation from the circumferential surface of a wafer set on the ceramic susceptor, the temperature of the wafer periphery is liable to be low compared with the wafer interior. As a consequence, the thermal radiation from the wafer circumferential surface is likely to impair the isothermal quality of the wafer face, and this problem has grown pronounced as the enlargement in diametric span progresses.
A further problem is that if a process is performed on the ceramic susceptor to form screw holes in it, with those portions as engendering points, cracking is liable to arise in the susceptor in the course of heating wafers. To eliminate any separation between the susceptor face on its wafer-retaining side and a wafer is therefore why the susceptor face in particular has been rendered a simple plane without subjecting it to any special process.